A plastic lens has light weight and is excellent in impact resistance as compared to glass, but is insufficient in surface hardness, and therefore the abrasion resistance thereof is enhanced by covering the surface thereof with various kinds of hard coat layers.
A hard coat layer generally has a refractive index in a range of from 1.40 to 1.55, and a plastic lens substrate generally has a refractive index of 1.50 or more. In the case where the difference in refractive index between the hard coat layer and the plastic lens substrate is large, no problem may occur when the hard coat layer has a uniform thickness, but when the hard coat layer has an uneven thickness, interference fringes are formed to impair the appearance of the lens, which may displease the user. However, it is considerably difficult to make a hard coat layer that has a uniform thickness, from the standpoint of manufacture.
Under the circumstances, there have been proposals of providing a λ/4 layer between the hard coat layer and the substrate (see PTLs 1 to 3). The λ/4 layer has a material having a refractive index in a particular range, and has a suitable film in consideration of the wavelength of visible light corresponding to the refractive index of the material. The λ/4 layer provided may prevent interference fringes from being formed.